1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to a light emitting apparatus and a control method thereof, and more particularly, to a light emitting apparatus, which is capable of separately controlling luminescence of a plurality of light emitting parts with a variety of gray scales, and a control method thereof.
2. Description of the Related Art
A light emitting apparatus includes a plurality of light emitting parts such as an array of light emitting diodes (LEDs) arranged in the form of a matrix, and a display such as a liquid crystal display (LCD) panel. The plurality of light emitting parts functions as a light source to allow an image to be displayed on the display.
FIGS. 5A and 5B are views showing examples of a conventional light emitting apparatus. As shown in FIG. 5A, the conventional light emitting apparatus includes 9 LEDs 10a to 10c, 20a to 20c, and 30a to 30c arranged in the form of a 3×3 matrix, and driving circuits 11a to 11c, 21a to 21c, and 31a to 31c for controlling the 9 LEDs 10a to 10c, 20a to 20c, and 30a to 30c, respectively. The light emitting apparatus can control the luminescence of the 9 LEDs 10a to 10c, 20a to 20c, and 30a to 30c sequentially by the driving circuits 11a to 11c, 21a to 21c, and 31a to 31c. The 9 LEDs 10a to 10c, 20a to 20c, and 30a to 30c may be monochromatic, or may represent a variety of colors in combination of LEDs of several colors.
The driving circuits 11a to 11c, 21a to 21c, and 31a to 31c, which are respectively assigned to the 9 LEDs 10a to 10c, 20a to 20c, and 30a to 30c, are applied with respective independent signals, and accordingly, the 9 LEDs 10a to 10c, 20a to 20c, and 30a to 30c emit light separately. Accordingly, in the light emitting apparatus, the LEDs 10a to 10c, 20a to 20c, and 30a to 30c can emit light with a certain luminescence to display a desired image on a display.
However, in the above-configured light emitting apparatus, the number of driving circuits and the number of driving signals increase as the number of LEDs increase. Therefore, if the LEDs are arranged with uniform density, as the area increases, the number of driving circuits and the number of driving signals may increase by geometric progression in proportion to the square of the area, which may make the light emitting apparatus impractical to use.
As another example, as shown in FIG. 5B, the light emitting apparatus may include 9 LEDs 12a to 12c, 22a to 22c, and 32a to 32c arranged in the form of a 3×3 matrix, three driving circuits 13a to 13c for controlling columns of the 9 LEDs 12a to 12c, 22a to 22c, and 32a to 32c, respectively, and three switches 14, 24 and 34 for controlling rows of the 9 LEDs 12a to 12c, 22a to 22c, and 32a to 32c, respectively.
In the light emitting apparatus, the three switches 14, 24 and 34 are sequentially turned on at a certain interval, and accordingly, a driving current is applied to the 9 LEDs 12a to 12c, 22a to 22c, or 32a to 32c at a turned-on row, thus emitting light therefrom. After the LEDs 32a to 32c at the last row emit light, the LEDs 12a to 12c at the first row emit light again. In this case, when the LEDs at each row are sequentially driven at a very high speed, it appears to a user that the LEDs are simultaneously driven with different luminescence since the user does not perceive fast variation of light but average luminescence (hereinafter referred also to as “brightness”) of varying light.
The light emitting apparatus as configured above has an advantage of simplicity of circuit configuration in that it requires only the number of driving circuits and driving signals corresponding to the number of LEDs in one row. However, with such configuration, since the LEDs corresponding to only one row emit light every moment, the use efficiency of the LEDs is low, that is, the maximum luminescence of the overall array of LEDs, which is perceivable by the user, is obtained by dividing the maximum luminescence of one LED by the number of rows. In order to overcome such a disadvantage, there may be a method of providing two or more groups of switches and driving LEDs belonging to each group simultaneously. However, this method also has a problem in that the number of driving circuits and the number of driving signals increase as the number of groups of switches increase.